Fluidic pressure-insensitive oscillator

ABSTRACT

The subject fluidic oscillator means includes a pair of bistable amplifiers having feedback control lines selected and connected in a manner to render the resulting device relatively insensitive to variations in the fluid pressure supply. The control signal ports of each amplifier are connected with the output ports of the other amplifier by conductors of predetermined differential length-to-area and volume ratios so selected and combined as to counteract the effects of supply pressure change, thus securing the above-mentioned result.

United States Patent Trevor G. Sutton Tempe, Ariz.

June 13, 1968 Apr. 20, 1971 The Garrett Corporation Los Angeles, Calif.

Inventor App]. No. Filed Patented Assignee FLUlDlC PRESSURE-INSENSITIVE OSCILLATOR 6 Claims, 6 Drawing Figs.

US. Cl

Int. Cl Field of Search.....

137/8l.5 Fl5c l/08 137/815 References Cited UNITED STATES PATENTS 7/1963 Joesting 3,185,166 5/1965 Horton et al 137/815 3,402,727 9/1968 Boothe 137/815 3,443,574 5/1969 Posingies... 137/815 3,474,805 10/1969 Swartz 137/815 Primary Examiner-William R. Cline Att0rneysHerSchel C. Omohundro and John N. l-lazelwood ABSTRACT: The subject fluidic oscillator means includes a pair of bistable amplifiers having feedback control lines selected and connected in a manner to render the resulting device relatively insensitive to variations in the fluid pressure supply. The control signal ports of each amplifier are connected with the output ports of the other amplifier by conductors of predetermined differential length-to-area and volume ratios so selected and combined as to counteract the effects of supply pressure change, thus securing the abovementioned result.

FREQUENCY H, 8 8f i 8 DEVIATION OF FREQUENCY FROM 20 PSI FREQUENCY pmmmo m SHEET 2 OF 2 5 I6 I 5 25 25 T3 SUPPLY PRESSURE PSIGY FIG.5

mvsmon TREVOR G. SUTTON SUPPLY PRESSURE (P PSIG ORNEY ll ll' LlllllllilllC lPSURE-INSENSHTIWE OSCUJLATOR SUMMARY This invention relates generally to the fluidic art and more particularly to oscillator means for use in fluidic circuits. More specifically, this invention pertains to oscillators of the feedback type and a scheme for reducing or eliminating the sensitivity of such mechanism to variations in supply pressure.

Ordinarily, a fluidic feedback oscillator includes a bistable amplifier having a main inlet for receiving fluid from a source and directing a power stream generally toward a pair of output ports. A control inlet on either side of the main inlet receives a pressure fluid feedback from one of the output ports and directs a control stream against the power stream to deflect it toward one or the other output port.

in the operation of the oscillator, alternate output ports receive the power stream and direct feedback signals to the control inlets to cause repeated switching of the power stream and intermittent or pulsating flow in the lines leading from the output ports. The frequency of pulsation ordinarily depends, in part, on the supply source pressure. To avoid change in frequency heretofore, it has been necessary to maintain the supply pressure sufficiently high to choke the main inlet port. This is a requirement because a feedback oscillator is basically by its nature pressure sensitive due to the flow characteristics of the amplifier and the feedback line, or lines, used. Since the characteristics of the amplifier are tired, the only portion subject to variation is the feedback line. The characteristics of such feedback lines are affected by both length and area and consequently volume. A line having a relatively short length but large area has orifice flow characteristics while a line with a relatively small area and a length at least a predetermined number of times its diameter will have capillary flow characteristics. i

It has been recognized that when a feedback line with a large length-to-area ratio and small volume is used in a fluidic oscillator, the oscillation frequency decreases with pressure, and that the opposite result is exhibited when a small lengthto-area ratio feedback line and large volume is employed. The recognition of this fact prompted the thought that by combining the lines the net effect secured would be an extension of the pressure-insensitive range of the oscillator in excess of that which may be achieved by the conventional practice of using supply pressure high enough to choke" the power nozzle. it has been discovered that by providing a double amplifier design and utilizing a particular arrangement of large length-to-area and small length-to-areQa ratio feedback lines, a pressure-insensitive fluidic oscillator means will result.

The oscillator means is made pressure insensitive by combining the effects of a capillary flow feedback line which has a characteristic of decreasing frequency with pressure level increase and an orifice flow feedback line which has the opposite effect. The orifice flow feedback line also has a large volume-to-length ratio, thus giving a capacitive effect, while the capillary line has small volume-to-length ratio representing mainly an inductive effect. However, the large volume or capacitance effect is a stronger function than the inductive effect; therefore, the inductive effect may be turned into a capacitance effect by introducing a volume in series with it. Thus, similar length-to-area (large) ratio lines may be used for each pair of feedback paths and a volume may be introduced into one pair of paths to obtain the required effect. This volume could be variable and thereby used to set the pressure-insensitive range. Such means will be particularly adaptable as a reference frequency for fluidic pulse controls because of its stability. It is also possible to make the oscillator means of this invention insensitive to temperature change over a given range by the incorporation of the small tapered duct principle whereby the complex speed of sound may be held constant with temperature change. A complete reference frequency for all fluidic pulse or frequency control applications will thus be secured. It is an object of this invention to provide such a combination of mechanisms.

A further object of the invention is to provide a fluidic oscillator means having first and second bistable amplifiers with output ports and control inlet ports connected by lines having differential length-to-area ratios such that the resulting combination will be relatively insensitive to variations in pressure at the fluid source.

A still further object of the invention is to provide a fluidic oscillator means having a pair of bistable amplifiers with the usual output and control inlet ports and in which the output ports of one amplifier are connected with the control inlet ports of the other amplifier bylines having large length-toarea ratio with predetermined volume, and the output ports of the latter amplifier'are connected with the control inlet ports of the first-mentioned amplifier by lines having small lengthto-area ratios and different predetermined volumes. Inthis manner, desirable flow characteristics of the feedback lines will be combined to cause the device to operate in such a way as to be unaffected by change in supply pressure within a predetennined range.

Other objects will be made apparent by the following description of portions of fluidic systems embodying devices formed in accordance with the present invention and schematically illustrated in the accompanying drawings.

THE DRAWINGS FIG. 1 is a schematic view of a substantially conventional bistable fluidic oscillator with feedback lines having a large length-to-area ratio;

FIG. 2 is a similar view in which the feedback lines have a small length-to-area ratio;

FIG. 3 represents a graph with curves showing a comparison of variation in frequency of the outputs of the oscillators shown in FIGS. 1 and 2 in response to supply pressure variations;

FIG. 4 is a schematic view of a fluidic oscillator means formed in accordance with the present invention;

FIG. 5 represents a graph with a curve to show the substantial uniformity of frequency of the output of the oscillator means of FIG. 4, irrespective of variations in supply pressures;

. and

FIG. 6 is a graph with a plurality of curves resulting from oscillators with feedback lines having a variety of length ratios to show the percent of deviation of frequency from a predetermined value.

DESCRIPTION Particular reference to FIGS. 1 to 3, inclusive, shows that these FIGS. illustrate substantially conventional fluidic oscillator constructions. Each of FIGS. 1 and 2 shows a bistable fluidic oscillator 10 having the usual supply inlet 11, separate output ports 12 and 13, and control inlet ports 14 and E5. The fluid pressure supplied to the control ports is withdrawn from the outlet ports through feedback passages 16 and 17 in FIG. 1, and through 21 and 22 in FIG. 2, respectively, leading to the control ports.

In FIG. 1, lines 16 and 17 are formed with large length-toarea ratios. This feature is accentuated by disposing capacitance chambers 18 in the feedback lines. The output ports are connected by suitable ducts 20 with transducers or other utilizing equipment. In FIG. 2, the same elements are present as in FIG. 1, however, the feedback lines 21 and 22 have small length-to-area ratios. To obtain this feature the same constant bore may be employed, but the length is changed. The feedback lines extend from the outlet ports to the control ports, as in FIG. 1. Also, the output ducts 20 lead to loading or utilizing equipment such as transducers 23. The operations of the circuits shown in FIGS. 1 and 2 are substantially conventional.

FIG. 3 is a graph with curves A and B, which show on the scales at the left and right sides, respectively, of the FIG. the frequencies of the output signals of the oscillators of FIGS. 1 and 2 relative to the supply pressures. It will be apparent from FIG. 3 that substantial variations in output signal frequencies result when the supply pressure changes in both of the oscillators. The output signals of the oscillator with the feedback lines having a large length-to-area ratio (see FIG. 1) have a low frequency at low supply pressure, and the frequency increases as the supply pressure is increased up to a predetermined maximum, after which the frequency decreases. The results secured from the other oscillator are somewhat opposite, i.e. the output signal frequency is high at low supply pressure and decreases as the supply pressure increases. The frequencies substantially stabilize when sufficient fluid pressure is supplied to choke the inlet ports.

As pointed out in the objects, the purpose herein is to combine the small and large length-to-area ratio feedback lines to secure output signals with substantially uniform frequencies regardless of the supply pressure. The manner of combining them is illustrated in FIG. 4. In this FIG., two bistable amplifiers 24 and 25 are provided. Each is supplied with fluid under pressure from a source, as at 26. Each of the amplifiers includes a pair of output ports, 27--30, incl. Each of the amplifiers has a pair of control inlets 31-34, incl. The control inlets for the amplifier 24 are connected by feedback lines 35 and 36 with the output ports 29 and 30, respectively, of amplifier 25. The control inlet ports 33 and 34 of the latter amplifier are connected by lines 37 and 38 with the output ports 27 and 28 of amplifier 24. Lines 37 and 38 are of a contrasting length-to-area ratio from that of the lines used to supply the control ports of amplifier 24. In this manner the effect of combining small and large length-to-area ratio feedback lines is secured.

The output passages 39 and 40 receive and convey to a suitable destination output signals which are substantially uniform in frequency, irrespective of the variation in pressure supplied to the inlets of the amplifiers. It is obvious that some minimum pressure must be provided to effect the operation of an amplifier.

FIG. is a graph with a curve C showing the substantial uniformity of frequency of the output signals of the oscillator means composed of the dual bistable amplifiers and contrasting length-to-area ratio feedback lines of FIG. 4. A careful examination of FIG. 5 will show a variation of approximately 10,5 percent. This stability is due entirely to the combination of feedback lines. One or the other or both of the passages leading from the output ports of the oscillator may be provided with a resistance 41 in advance of the utilizing mechanism to limit the extent of the pulsations.

FIG. 6 is a graph showing a plurality of curves resulting from feedback lines with a variety of length-to-area ratios. This FIG. shows the percent ofdeviation of output signal frequency from a nominal frequency at p.s.i. In FIG. 6, curves have been shown for various feedback linelength ratios A/B,

considering the feedback line 38 of FIG. 4 as A and the feedback line 36 of the same FIG. as B, as follows:

all of the feedback lines having the same cross-sectional area. These curves show that the variation or deviation from a set point designated 0 changes little after a predetermined supply pressure is reached, even though the supply pressure varies considerably. The dotted curve designated 5/10 ratio is typical of feedback lines having the most desirable ratio of length-toarea ratios.

I claim:

1. An inlet pressure-insensitive fluidic oscillator means,

comprising:

a. first and second bistable amplifiers, each having a main jet nozzle for receiving fluid under variable supply pressure and creating a power stream, a pair of output ports, and a controljet nozzle at each side of said main jet nozzle for applying control streams to said power stream to deflect the same and vary the proportion of fluid discharged through said output ports; and b. a set 0 passages leading from the output ports of each amplifier to the control jet nozzles of the other amplifier, one set of passages being arranged in inverse relationship to the other set and one set being constructed to have orifice flow characteristics and the other set being constructed to have capillary flow characteristics.

2. The inlet pressure-insensitive fluidic oscillator means of claim 1 in which the output ports of each amplifier communicate with the control jet nozzles of the other amplifier via passages having substantially equal cross-sectional areas, the passages leading from the output ports of one amplifier being of greater length than the passages leading from the output ports of the other amplifier.

3. The pressure-insensitive fluidic oscillator means of claim 2, in which the passages of the first set have a greater length than the passages of the second set.

4. The inlet pressure-insensitive fluidic oscillator means of claim 3 in which the output ports of the second amplifier communicate with load orifices downstream of the points of communication of the passages of said second set therewith.

5. The inlet pressure-insensitive fluidic oscillator means of claim 2 in which the ratio of the length of the passages leading from one amplifier relative to the length of the passages leading from the other amplifier is substantially 5/30.

6. The inlet pressure-insensitive fluidic oscillator means of claim 1 in which the output ports of the second amplifier communicate with the control jet nozzles 0f the first amplifier via passages having relatively small length-to-area and volume ratios. 

1. An inlet pressure-insensitive fluidic oscillator means, comprising: a. first and second bistable amplifiers, each having a main jet nozzle for receiving fluid under variable supply pressure and creating a power stream, a pair of output ports, and a control jet nozzle at each side of said main jet nozzle for applying control streams to said power stream to deflect the same and vary the proportion of fluid discharged through said output ports; and b. a set of passages leading from the output ports of each amplifier to the control jet nozzles of the other amplifier, one set of passages being arranged in inverse relationship to the other set and one set being constructed to have orifice flow characteristics and the other set being constructed to have capillary flow characteristics.
 2. The inlet pressure-insensitive fluidic oscillator means of claim 1 in which the output ports of each amplifier communicate with the control jet nozzles of the other amplifier via passages having substantially equal cross-sectional areas, the passages leading from the output ports of one amplifier being of greater length than the passages leading from the output ports of the other amplifier.
 3. The pressure-insensitive fluidic oscillator means of claim 2, in which the passages of the first set have a greater length than the passages of the second set.
 4. The inlet pressure-insensitive fluidic oscillator means of claim 3 in which the output ports of the second amplifier communicate with load orifices downstream of the points of communication of the passages of said second set therewith.
 5. The inlet pressure-insensitive fluidic oscillator means of claim 2 in which the ratio of the length of the passages leading from one amplifier relative to the length of the passages leading from the other amplifier is substantially 5/30.
 6. The inlet pressure-insensitive fluidic oscillator means of claim 1 in which the output ports of the second amplifier communicate with the control jet nozzles of the first amplifier via passages having relatively small length-to-area and volume ratios. 